Massive stars as cosmic engines

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MASSIVE STARS AS COSMIC ENGINES Massive stars comprise all stars initially above 8 solar masses, that collapse as supernovae at the end of their nuclear-burning lives, leaving behind neutron stars or black holes. Since the light output of a normal star goes as the cube of its mass, a single, 100 solar-mass star can match the total light from a million Suns. Above 20 solar masses, massive stars further distinguish themselves by their strong winds, ranging up to a billion times that of the Sun.  Thus, although rare and short-lived, massive stars deliver huge quantities of radiation, mostly as lethal ultraviolet, and enriched material to the interstellar medium, ready to build more stars and planets like Earth.  This was especially important in the early Universe, when the first stars formed were probably all very massive. The main goals of this program are to explore: (1) if radiation pressure alone can drive the extreme winds of the pre-supernova, He-burning WR phase, using the first Canadian space telescope on board the microsatellite MOST, (2) building a nanosatellite to systematically probe the low-amplitude instability properties of a large number of bright, massive stars, (3) the exact way in which the winds expand in luminous, hot stars, (4) the role of magnetic fields in accelerating the winds, (5) the puzzle of how dust grains form and survive in the hostile environments of hot, luminous stars, (6) the upper mass cut-off for the most massive stars (is it 100, 150, or 200 solar masses?), (7) the content of WR stars in our whole Galaxy, mostly hidden by interstellar dust, and (8) whether WR stars actually explode as supernovae, leading in some cases to the most energetic (although short-lived) phenomenon in the Universe, the long gamma-ray bursts.